The present invention relates to a dental chair comprising a lower part, and an upper part, the upper part having an inclinable seat part and a tiltable backrest, seat part and backrest being pivotally attached together, and the seat part and backrest also being connected with the lower part of the chair at a common point of support and having interdependent movements which take place by means of a common actuating member acting on seat part and backrest via a linkage system.
By means of such a dental chair the dentist should be able to bring the patient into any position appropriate for any necessary and/or desired type of treatment. By coupling together the inclining of the seat part and the tilting of the backrest, it is only necessary to control two drives, one for adjusting the backrest and the seat about a horizontal axis running through the common support and along the longitudinal axis, and one for adjusting the vertical height of the upper part with respect to the lower part.
Dental chairs of the foregoing type are already known but are so constructed that tilting the seat takes place only upon completion of the movement of the backrest and with a relatively high angular velocity. Chairs with separate drives, one for tilting the backrest and the other for tilting the seat, make a tilting possible which is more appropriate from the dentist's point of view, especially with electronic control, but such chairs are costly to construct and thus are expensive.
The drawback associated with the seat tilting at the end of the tilting movement of the backrest is that the patient may suddenly slip off the seat if the so-called "collapse" position is assumed (an extreme prone position wherein the head is lower than the heart), especially when the collapse is carried out during the treatment of the patient while in the sitting position. This means that in the case of an adjustment from the sitting position into the prone position, the angle between seat and backrest should increase only so far that the patient is relaxed, while if the adjustment is continued to the start of a collapse position the seat should not move additionally while the backrest continues to lower and thus assure the the patient remains safely on the chair. Furthermore, in many known dental chairs the seats are raised, depending on construction, by a cam or a roller, which are used by almost all chairs in the adjusting mechanism of the seat, and this can cause additional difficulty regarding the secure position of the patient, especially during the descent into the collapse position.